1. Field of the Invention
The present invention relates to cured dielectric films and to a process for the treatment of the surface of such films to remove moisture and other contaminants therefrom. Such treatment is done by electron beam exposure of the dielectric surface in order to prepare it for a subsequent chemical vapor deposition of oxide, nitride or oxynitride layers. These films are useful in the manufacture of integrated circuits.
2. Description of the Related Art
The field of semiconductor technology continually requires the formation of integrated circuit chips having more and faster circuits thereon. Such ultralarge scale integration has resulted in a continued shrinkage of feature sizes with the result that a large number of devices are available on a single chip. With a limited chip surface area, the interconnect density typically expands above the chip substrate in a multi-level arrangement and therefore the devices have to be interconnected across these multiple levels.
The interconnects must be electrically insulated from each other except where designed to make electrical contact. Usually electrical insulation requires depositing dielectric films onto a surface. It is known in the art that a variety of resins are useful in the semiconductor fields to provide a dielectric coating to silicon wafers and other microelectronic devices. Such coatings protect the surface of substrates and form dielectric layers between electric conductors on integrated circuits. Semiconductor devices have multiple arrays of patterned interconnect levels that serve to electrically couple individual circuit elements thus forming the integrated circuit.
In the processing of microelectronic devices, dielectric layers are typically subjected to planarizing and etching treatments and hence adjacent layers are usually separated by an etch stop or other separation layer. Etch stop layers usually comprises an oxide, nitride or oxynitride film such as a silicon oxide film formed using chemical vapor deposition (CVD) or plasma enhanced CVD (PECVD) techniques. However, the application of such films to dielectric layers has become a problem. This is due to moisture and contaminants such as organic solvents, hydrocarbons and stray particles on the dielectric surface.
It has now been found that such moisture and contaminants can be eliminated from the surface of dielectric films by exposing the surface of the dielectric to electron beam radiation. Such electron beam exposure effectively removes these contaminants and allows the surface to more readily accept chemical vapor deposited oxide, nitride or oxynitride films.
The invention provides a process for treating a dielectric layer on a substrate which comprises
(a) heating a surface of the dielectric layer and exposing the dielectric layer to electron beam irradiation under vacuum conditions, for a sufficient time, temperature, electron beam energy and electron beam dose to remove substantially all moisture and/or contaminants from the surface of the dielectric layer; and
(b) chemical vapor depositing a chemical vapor deposit material onto the surface of the dielectric layer while maintaining said vacuum conditions.
The invention also provides a process for producing a support for a microelectronic device which comprises:
(a) applying a dielectric layer onto a substrate;
(b) curing the dielectric layer;
(c) heating a surface of the dielectric layer and exposing the dielectric layer to electron beam irradiation under vacuum conditions, for a sufficient time, temperature, electron beam energy and electron beam dose to remove substantially all moisture and/or contaminants from the surface of the dielectric layer; and
(d) chemical vapor depositingchemical vapor deposit material onto the surface of the dielectric layer while maintaining said vacuum conditions.
The invention further provides a A support for a microelectronic device which comprises:
(a) a substrate;
(b) a cured dielectric layer on the substrate, the surface of which dielectric layer has been exposed to sufficient electron beam radiation to render the dielectric layer surface substantially devoid of moisture and contaminants; and
(c) a chemical vapor deposited chemical vapor deposit material on the surface of the dielectric layer.
The invention also provides a microelectronic device which comprises:
(a) a substrate;
(b) a cured dielectric layer on the substrate, the surface of which dielectric layer has been exposed to sufficient electron beam radiation to render the dielectric layer surface substantially devoid of moisture and contaminants;
(c) a chemical vapor deposited chemical vapor deposit material layer on the surface of the dielectric layer; and
(d) a pattern of conductive lines on the chemical vapor deposit material layer.
The first step in conducting the process of the present invention is to form a dielectric composition layer on a substrate. Typical substrates are those suitable to be processed into an integrated circuit or other microelectronic device. Suitable substrates for the present invention non-exclusively include semiconductor materials such as gallium arsenide (GaAs), germanium, lithium niobate, silicon and compositions containing silicon such as silicon germanium, crystalline silicon, polysilicon, amorphous silicon, epitaxial silicon, and silicon dioxide (SiO2) and mixtures thereof.
On the surface of the substrate is an optional pattern of raised lines, such as metal, oxide, nitride or oxynitride lines which are formed by well known lithographic techniques. Suitable materials for the lines include silica, silicon nitride, titanium nitride, tantalum nitride, aluminum, aluminum alloys, copper, copper alloys, tantalum, tungsten and silicon oxynitride. These lines form the conductors or insulators of an integrated circuit. Such are typically closely separated from one another at distances of about 20 micrometers or less, preferably 1 micrometer or less, and more preferably from about 0.05 to about 1 micrometer.
The dielectric composition may comprise any of a wide variety of dielectric forming materials which are well known in the art for use in the formation of microelectronic devices. Such may be organic or inorganic. The dielectric layer may nonexclusively include silicon containing spin-on glasses, i.e. silicon containing polymer such as an alkoxysilane polymer, a silsesquioxane polymer such as a hydrogen silsesquioxane polymer, a siloxane polymer; a poly(arylene ether), a fluorinated poly(arylene ether), other polymeric dielectric materials, nanoporous silica or mixtures thereof.
One useful polymeric dielectric materials useful for the invention includes a nanoporous silica alkoxysilane polymer formed from an alkoxysilane monomer which has the formula: 
wherein at least 2 of the R groups are independently C1 to C4 alkoxy groups and the balance, if any, are independently selected from the group consisting of hydrogen, alkyl, phenyl, halogen, substituted phenyl. Preferably each R is methoxy, ethoxy or propoxy. Such are commercially available from AlliedSignal as Nanoglass(trademark). The most preferred alkoxysilane monomer is tetraethoxysilane (TEOS). Also useful are hydrogensiloxanes which have the formula [(HSiO1.5)xOy]n, hydrogensilsesquioxanes which have the formula (HSiO1.5)n, and hydroorganosiloxanes which have the formulae [(HSiO1.5)xOy(RSiO1.5)z]n, [(HSiO1.5)x(RSiO1.5)y]n, and [(HSiO1.5)xOy(RSiO1.5)z]n. In each of these polymer formulae, x=about 6 to about 20, y=1 to about 3, z=about 6 to about 20, n=1 to about 4,000, and each R is independently H, C1, to C8 alkyl or C6 to C12 aryl. The weight average molecular weight may range from about 1,000 to about 220,000. In the preferred embodiment n ranges from about 100 to about 800 yielding a molecular weight of from about 5,000 to about 45,000. More preferably, n ranges from about 250 to about 650 yielding a molecular weight of from about 14,000 to about 36,000. Useful polymers within the context of this invention nonexclusively include hydrogensiloxane, hydrogensilsesquioxane, hydrogenmethylsiloxane, hydrogenethylsiloxane, hydrogenpropylsiloxane, hydrogenbutylsiloxane, hydrogentert-butylsiloxane, hydrogenphenylsiloxane, hydrogenmethylsilsesquioxane, hydrogenethylsilsesquioxane, hydrogenpropylsilsesquioxane, hydrogenbutylsilsesquioxane, hydrogentert-butylsilsesquioxane and hydrogenphenylsilsesquioxane and mixtures thereof. Useful organic polymers include polyimides, fluorinated and nonfluorinated polymers, in particular fluorinated and nonfluorinated poly(arylethers) available under the tradename FLARE(trademark) from AlliedSignal Inc., and copolymer mixtures thereof. The hydroorganosiloxanes, poly(arylene ethers), fluorinated poly(arylene ethers) and mixtures thereof are preferred. Suitable poly(arylene ethers) or fluorinated poly(arylene ethers) are known in the art from U.S. Pat. Nos. 5,155,175; 5,114,780 and 5,115,082. Preferred poly(arylene ethers) and fluorinated poly(arylene ethers) are disclosed in U.S. patent application Ser. No. 08/990,157 filed Dec. 12, 1997 which is incorporated herein by reference. Preferred siloxane materials suitable for use in this invention are commercially available from AlliedSignal Inc. under the tradename Accuglass(copyright) T-11, T-12 and T-14. Also useful are methylated siloxane polymers available from AlliedSignal Inc. under the tradenames Purespin(trademark) and Accuspin(copyright) T18, T23 and T24.
Preferred silicon containing dielectric resins include polymers having a formula selected from the group consisting of [(HSiO1.5)xOy]n,(HSiO1.5)n, [(HSiO1.5)xOy(RSiO1.5)z]n, [(HSiO1.5)x(RSiO1.5)y]n and [(HSiO1.5)xOy(RSiO1.5)z]n wherein x=about 6 to about 20, y=1 to about 3, z=about 6 to about 20, n=1 to about 4,000, and each R is independently H, C1 to C8 alkyl or C6 to C12 aryl which are disclosed in U.S. patent application Ser. No. 08/955,802 filed Oct. 22, 1997 and which is incorporated herein by reference. Also preferred are certain low organic content silicon containing polymers such as those having the formula I:
[Hxe2x80x94SiO1.5]n[Rxe2x80x94SiO1.5]m,
[H0.4xe2x80x94SiO1.5-1.8]n[R0.4-1.0xe2x80x94SiO1.5-1.8]m,
[H0-1.0xe2x80x94SiO1.5-2.0]n[Rxe2x80x94SiO1.5]m,
xe2x80x83[Hxe2x80x94SiO1.5]x[Rxe2x80x94SiO1.5]y[SiO2]2,
wherein the sum of n and m, or the sum or x, y and z is from about 8 to about 5000, and m and y are selected such that carbon containing substituents are present in an amount of less than about 40 Mole percent. Polymers having the structure I are of low organic content where the carbon containing substituents are present in an amount of less than about 40 mole percent. These polymers are described more fully in U.S. patent application Ser. No. 09/044,831, filed Mar. 20, 1998, which is incorporated herein by reference. Also preferred are certain low organic content silicon containing polymers such as those having the formula II:
[HSiO1.5]n[RSiO1.5]m,
[H0.4-1.0SiO1.5-1.8]n[R0.4-1.0SiO1.5-1.8]m,
[H0-1.0SiO1.5-2.0]n[RSiO1.5]m,
wherein the sum of n and m is from about 8 to about 5000 and m is selected such that the carbon containing substituent is present in an amount of from about 40 Mole percent or greater; and
[HSiO1.5]x[RSiO1.5]y[SiO2]z;
wherein the sum of x, y and z is from about 8 to about 5000 and y is selected such that the carbon containing substituent is present in an amount of about 40 Mole % or greater; and wherein R is selected from substituted and unsubstituted straight chain and branched alkyl groups, cycloalkyl groups, substituted and unsubstituted aryl groups, and mixtures thereof. The specific mole percent of carbon containing substituents is a function of the ratio of the amounts of starting materials. Polymers having the structure II which are of high organic content where the carbon containing substituents are present in an amount of about 40 mole percent or more. These polymers are described more fully in U.S. patent application Ser. No. 09/044,798, filed Mar. 20, 1998, which is incorporated herein by reference.
The dielectric polymer may be present in the dielectric composition in a pure or neat state (not mixed with any solvents) or it may be present in a solution where it is mixed with solvents. Preferably the dielectric polymer is dispersed in a suitable compatible solvent and applied onto a substrate. Suitable solvent compositions include those which have a boiling point of about 120xc2x0 C. or less, preferably about 100xc2x0 C. or less. Suitable solvents nonexclusively include methanol, ethanol, n-propanol, isopropanol, n-butanol; aprotic solvents such as cyclic ketones including cyclopentanone, cyclohexanone and cyclooctanone; cyclic amides such as N-alkylpyrrolidinone wherein the alkyl group has from 1 to about 4 carbon atoms, and N-cyclohexyl-pyrrolidinone, and mixtures thereof. Other relatively high volatility solvent compositions which are compatible with the other ingredients can be readily determined by those skilled in the art. When solvents are present, the polymer is preferably present in an amount of from about 1% to about 50% by weight of the polymer, more preferably from about 3% to about 20%. The solvent component is preferably present in an amount of from about 50% to about 99% by weight of the dielectric composition, more preferably from about 80% to about 97%.
Once formed, the dielectric composition is deposited onto a substrate to thereby form a dielectric polymer layer on the substrate. Deposition may be conducted via conventional spin-coating, dip coating, roller coating, spraying, chemical vapor deposition methods, or meniscus coating methods which are well-known in the art. Spin coating is most preferred. The thickness of the polymer layer on the substrate may vary depending on the deposition procedure and parameter setup, but typically the thickness may range from about 500 xc3x85 to about 50,000 xc3x85, and preferably from about 2000 xc3x85 to about 12000 xc3x85. The amount of dielectric composition applied to the substrate may vary from about 1 ml to about 10 ml, and preferably from about 2 ml to about 8 ml. In the preferred embodiment, the liquid dielectric composition is spun onto the upper surface the substrate according to known spin techniques. Preferably, the polymer layer is applied by centrally applying the liquid dielectric composition to the substrate and then spinning the substrate on a rotating wheel at speeds ranging from about 500 to about 6000 rpm, preferably from about 1500 to about 4000 rpm, for about 5 to about 60 seconds, preferably from about 10 to about 30 seconds, in order to spread the solution evenly across the substrate surface. The polymer layer preferably has a density of from about 1 g/cm3 to about 3 g/cm3.
In an optional but preferred step, the treated wafer substrate is then heated for a time and at a temperature sufficient to evaporate the solvents from the film or to cure the film. This may be conducted, for example by a hot plate heat treatment at a temperature of from about 170xc2x0 C. to about 320xc2x0 C. for about 10 seconds to about 5 minutes, preferably for from about 30 seconds to about 60 minutes. This is preferably done on a hot plate but may also be done in an oven. The heat treatment of the film crosslinks, solidifies and partially planarizes the layer. After the coating is heated, the thickness of the resulting film ranges from about 500 xc3x85 to about 50,000 xc3x85, preferably from about 500 xc3x85 to about 20,000 xc3x85, and most preferably from about 1,000 xc3x85 to about 12,000 xc3x85. The polymer layer may also optionally be cured by exposure to actinic light, such as UV light, to increase its molecular weight. The amount of exposure may range from about 100 mJ/cm2 to about 300 mJ/cm2.
The film may also be cured by exposing the surface of the substrate to a flux of electrons. Whether the film is cured by electron beam exposure or is cured by other means such as heating or exposure to UV light, the surface of the dielectric film is exposed to sufficient electron beam exposure to remove substantially all moisture and contaminants from the surface of the dielectric layer.
Such a treatment is performed by placing the substrate inside the chamber of a large area electron beam exposure system, such as that described in U.S. Pat. No. 5,003,178 to Livesay, the disclosure of which is incorporated herein by reference. This apparatus exposes the entire substrate to a flood electron beam flux all at once. The period of electron beam exposure will be dependent on the strength of the beam dosage, the electron beam energy applied to the substrate and the beam current density. One of ordinary skill in the art can readily optimize the conditions of exposure. Preferably the electron beam exposure is done at a vacuum in the range of from about 10xe2x88x925 to about 102 torr, and with a substrate temperature in the range of from about 25xc2x0 C. to about 1050xc2x0 C. When the electron beam is used both for dielectric curing and surface treatment, energy will fall into the range of from about 0.5 to about 30 KeV, preferably from about 1 to about 15 KeV and more preferably from about 1 to about 8 KeV.
When the electron beam is used both for dielectric curing and surface treatment, the electron beam dose will fall into the range of from about 1 to about 100,000 xcexcC/cm2, preferably from about 100 to about 10,000xcexcC/cm2, and more preferably from about 1 to about 8,000 xcexcC/cm2. The dose and energy selected will be proportional to the thickness of the films to be processed. When the electron beam is used as a dielectric surface treatment, energy and doses will fall into the ranges of about 0.5 to about 3 KeV and about 100 to about 5,000 xcexcC/cm2, respectively. The appropriate doses and energies may easily be determined by those skilled in the art for the case at hand. With the surface treatment, the electron beam is concentrated at a distance within about 1000 xc3x85 from the surface of the dielectric layer. The electron beam irradiation conditions are sufficient to remove substantially all moisture, hydrocarbons, organic solvents and particles on the surface of the dielectric layer and at a depth of up to about 1000 xc3x85 from the surface. Generally the exposure will range from about 0.5 minute to about 120 minutes, and preferably from about 1 minute to about 60 minutes. The dielectric coated substrate may be exposed to electron beams in any chamber having a means for providing electron beam radiation to substrates placed therein. The dielectric is preferably subjected to an electron beam radiation from a uniform large-area electron beam source under conditions sufficient to anneal the dielectric film. Preferably the exposure is conducted with an electron beam which covers an area of from about 4 square inches to about 256 square inches. The gaseous ambient in the electron beam system chamber may be nitrogen, hydrogen, argon, oxygen, or any combinations of these gases.
The treated dielectric surface is now conditioned for the reception of a chemical vapor deposited material such as a metal, oxide, nitride or oxynitride layer to the surface of the dielectric layer. Chemical vapor deposition processes are well known to those skilled in the art and chemical vapor deposition reactors are widely commercially available. One suitable reactor is model SK-23-6-93 commercially available from Vactronic Equipment Labs of Bohemia, New York. The surface of the dielectric is applied with a material such as silicon nitride, titanium nitride, tantalum nitride, tantalum oxynitride, tungsten oxynitride, silicon oxynitride and blends thereof. The oxide nitride or oxynitride layer is typically deposited over the dielectric on the substrate to a thickness of from about 200 to about 6,000 xc3x85.
Preferably the overall process of electron beam surface treatment and chemical vapor deposition is within a cluster tool having an electron beam irradiation chamber, a chemical vapor deposition chamber, and means for transferring the substrate from the electron beam irradiation chamber to the chemical vapor deposition chamber. The electron beam irradiation chamber, the chemical vapor deposition and the transferring from the electron beam irradiation chamber to the chemical vapor deposition chamber are conducted while continuously maintaining vacuum conditions. Such a cluster tool is described in U.S. patent application Ser. No. 09/272,869, filed Mar. 19, 1999 which is incorporated herein by reference. Wafers are continuously maintained in an isolated environment at a constant vacuum pressure level, and transferred into and out of an external atmospheric pressure environment through one or more access ports or load-locks. In a typical system, a cassette or carrier with a series of wafers is placed at an interface port of the cluster tool and latches release the port door. A manipulator robot picks up the cassette or individual wafers and directs them to desired processing stations within the equipment. After processing, the reverse operation takes place. Such a wafer processing technique essentially eliminates contaminates since treatment takes place after the wafers are sealed in the internal vacuum environment, and they are not removed prior to completion of processing. The configuration achieves a significant improvement over the conventional handling of open cassettes inside a clean room. In addition, since the vacuum is not broken from step to step, the use of cluster tools increases process productivity. The use of a cluster tool significantly aids semiconductor processing throughput. As a result, electron beam surface treatment and chemical vapor deposition can be done directly within a cluster tool without breaking vacuum or removal from the cluster tool.